Examples of the process for producing L-glutamine by a fermentation method include methods using a mutant strain imparted with amino acid analogue resistance, such as a method using a coryneform bacterium imparted with azaserine resistance (patent document 1), a method using coryneform bacterium imparted with 6-diazo-5-oxo-norleucine resistance (patent document 2) and the like, a method for increasing glutamine synthetase activity involved in the synthesis of L-glutamine and the like. Specific examples of known method for increasing glutamine synthetase activity involved in the synthesis of L-glutamine include decrease of the activity of glutamine synthetase adenylyltransferase which is a controller via adenylylation (non-patent document 1, patent document 3), substitution of the 405th amino acid residue of glutamine synthetase that is subject to adenylylation (non-patent document 1, patent document 4), decrease of a PII protein activity (non-patent document 2, patent document 3) and the like.
Examples of known process for producing L-glutamic acid according to the fermentation method include a method of culturing coryneform bacterium or a mutant strain thereof under biotin-limited conditions, and a method of culturing same with the addition of penicillin and a surfactant (non-patent document 3).
It has been clarified that a superhelical structure of chromosomal DNA plays an important role in controlling the synthesis of ribosomal RNA and transfer RNA in bacteria. DNA gyrase, which is one kind of type II DNA topoisomerase, has an activity to cleave and ligate double-stranded DNA, and converts positive superhelical DNA or relaxed DNA to negative superhelical DNA in the presence of ATP. It is known that, in a DNA gyrase mutant strain of Escherichia coli, the expression level of operon involved in L-histidine synthesis is increased and expression of some tRNAs including His-tRNA is decreased (non-patent document 4). On the other hand, type I DNA topoisomerase has an activity to cleave one chain of DNA and relaxes superhelical DNA.
Escherichia coli is known to show improved expression of His-tRNA and Tyr-tRNA once type I DNA topoisomerase becomes defective (non-patent document 5). Furthermore, this effect is known to be complemented by introduction of a plasmid in which a gene encoding a subunit of type I or IV DNA topoisomerase is cloned (non-patent document 5).
It is known that L-histidine producibility is increased by imparting resistance to a DNA gyrase inhibitor to Escherichia coli having L-histidine productivity (patent document 5). However, it is not known at all heretofore that an enzyme involved in DNA topology is involved in the improvement of productivity of amino acid other than L-histidine and modification of an enzyme involved in DNA topology can improve productivity of L-amino acid other than L-histidine such as L-glutamine, L-glutamic acid and the like.